1. Field of the Invention
The invention relates to the synthesis of tris and tetrakis aminium dyes. More particularly, the invention pertains to aminium dye precursors, as well as salts and near infrared (IR) dyes formed therefrom.
2. Description of the Related Art
Near IR dyes are well known in the art. The spectral properties of infrared light absorbing aminium dyes was first reported by Otto Neunhoeffer and Peter Heitmann (see Neunhoeffer et al., Chemische Berichte 92, 245-251 (1959) and Neunhoeffer et al., Chemische Berichte 94, 2511-2515 (1961)). Subsequent development of these dyes at the American Cyanamid Company of Stamford, Conn. by Peter Susi and colleagues is reported in U.S. Pat. Nos. 3,341,464, 3,440,257, 3,484,467, 3,575,871, 3,631,147, 3,637,769, 3,670,025 and 3,709,830 to Susi et. al., as well as U.S. Pat. No. 3,400,156 (Milionis et al.), U.S. Pat. No. 3,962,290 (Grosso) and U.S. Pat. No. 5,686,639 (Cohen et al.), the disclosures of which are incorporated herein by reference. Various other patents disclose methods of preparation of intermediates and the use of such aminium salts as near infrared dyes.
In general these dyes have the property of passing light in the visible portion of the spectrum (450 to 700 nanometers) and absorbing strongly in the near IR portion of the spectrum (900 to 1300 nanometers). By their use, it is possible to sequester about 35 to 50 percent of the sun's total energy. The amount is much higher when absorbing radiation from tungsten filament lamps. These dyes can be incorporated in a variety of plastics and can be used as sunglasses, welding shields, laser protection eyewear, windows, television filters, projection lenses and other products which can attenuate the heat from radiant sources or absorb specific laser radiation. As described in the referenced patents, the dye is incorporated into plastic film or sheet by molding the plastic with the dye, imbibing the dye into the preformed plastic sheet or by forming the sheet by cell casting and polymerizing the polymerizable monomer containing the dissolved dye.
Near infrared dyes are commonly synthesized from tris and tetrakis amines. These intermediates are converted into salts and oxidized to form dyes. For example, U.S. Pat. No. 3,709,830 provides p-Quinonediimonium salts and their use as infrared absorbers. This patent discloses the synthesis of N,N′,N″,N′″-tetrakis(4-[di(2-hydroxyethyl)amino]-phenyl)-p-benzoquinonebis(imonium hexafluoro-antimonate) by combining N,N′,N″,N′″-tetrakis(4-[di(2-hydroxyethyl)amino]phenyl)-p-phenylenediamine with methanol and silver hexafluoroantimonate. This SbF6 salt is not water-soluble and other salts have minimal water solubility. The present invention provides a new class of water-soluble, near infrared dyes that are obtained by the oxidation of carboxylic acid-modified tris or tetrakis amines. These dyes allow a similar maximization of the frequency range of absorption while at the same time allowing transmission in the visible range to be as transparent as possible. Further, one particular advantage offered by these water-soluble dyes is their very high solubility in mixed aqueous coating systems. These coatings are very thin (approx 0.5 mil to 1.0 mils). For example, if the concentration of dye used in an 80 mil optical lens requires 0.1 to 0.5% of near infrared dye, then a thin coating would need a concentration of dye 50-100 times as great, and approximately 4% by weight of dye in the dry coating weight would be used in such a coating. Accordingly, the present invention provides a solution to the existing needs in the art.